Influence of receiver surface spectral selectivity on the solar-to-electric efficiency of a solar tower power plant

Abstract

The spectral selectivity results in increasing the absorption of the incident solar flux and decreasing the radiative losses due to emission of heated walls. This study investigates the influence of the spectral selectivity on power generation efficiency of a central receiver solar concentrating system (solar power tower). A parametric study is conducted to quantify the potential efficiency gain that may result from spectral selectivity with the solar absorption, the cutoff wavelength, the infrared emissivity, the wall temperature and the receiver geometry (plane or cavity) as parameters. The model used to compute the receiver efficiency is based on a Monte Carlo ray-tracing algorithm for the radiative losses, the Clausing model for the convective losses and the Chambadal–Novikov–Curzon–Ahlborn approach for thermodynamic efficiency. The two tested receiver geometries are a plane receiver and a cubic cavity having the same cross section area of the aperture. State-of-the-art (metal alloys) and promising ceramic materials were studied such as SiC, ZrB2, ZrC and TaC. In the latter cases the native measured optical properties of carbides are considered. Finally, an intrinsic spectrally selective material such as TaC demonstrates promising results with global facility efficiency close to the maximum when solar absorptivity is enhanced by microstructuration, for example. As a conclusion, it is shown that spectral selectivity may result in an increase of overall solar power plant efficiency by about 6% (or 28% in relative value) with current state-of-the-art.